A typical cordless handheld surgical instrument uses a detachable and rechargeable battery pack to power the instrument. In most instances, the battery pack is attached to a bottom or base portion of the housing of the instrument. The housing or a motor controller module, which is contained within a handgrip portion of the housing, supports electrical contacts configured for coupling to the battery pack and delivering power through the motor controller module to the motor. Trigger controls, also contained within the handgrip portion of the housing, interface with the motor controller module for selectively delivering the power from the battery pack to the motor. In most instances, the motor control module is in close proximity to the electrical contacts of the instrument, for example, as illustrated in U.S. Pat. No. 7,638,958 to Philipp et al.
The motor controller module generally includes a processor portion and a power transmission portion. The power transmission portion is commonly composed of metal-oxide-semiconductor field-effect transistors (MOSFETs) which generate a large amount of heat during operation. This heat, in combination with the heat generated by the motor, can raise temperatures within the housing to 120 degrees C. or more. At these temperatures, the instrument's sensitive electronic circuitry, such as the circuitry of the motor control module, can suffer heat damage. If the heat is great enough, the heat can be transferred into the hand grip in sufficient amounts to cause discomfort for the operator of the device. Thus, a common failure mode in cordless, powered handheld surgical instruments is the over-heating of controller electronic components due to heat generated by the components, heat sensitivity of the components and the lack of an efficient means by which heat is dissipated from the controller module. To address the overheating of cordless handheld surgical instruments U.S. Pat. No. 7,211,347 to Sugiura et al. and U.S. Pat. No. 6,933,076 to Ura et al. describe equipping a battery housing with fins which function as a heat sink and heat spreader for the battery cells therein.